Cape Town - Eddie Jones believes that complacency will be England's biggest threat ahead of the 2017 Six Nations.
Jones named his 34-man squad for the tournament on Friday with England beginning their campaign against France on 4 February.
His side are on a 14-match unbeaten run, however, he says his squad must not lose focus.
"Complacency is our biggest challenge," Jones told the RFU website.
"We want to be confident but hardened. Hardened to the reality of what is in front of us."
He also warned about his players looking too far ahead with a British and Irish Lions tour to New Zealand on the horizon.
"If you read anything in the media all the players are talking about Lions or are always asked about the Lions," he said.
"It’s a massive attraction but it can be a massive distraction in terms of players focussing on the future rather than focussing on what is going on at the moment.
"The players have got to understand that going on a Lions tour is a consequence of playing well for England. If they play well for England they will be selected for the Lions."